Research On MEMS Flexible ECG Microneedle Arrays Dry Electrode

Traditional Ag/AgCI wet electrode as one of the surface electrodes is the most commonly used to acquire electrocardiogram(ECG)signals by medical equipment.To effectively reduce the electrode-to-skin contact impedance(ESCI),the wet electrodes used together with conductive gel can obtain the high-quality ECG signals in a short term.But the problems of dry conductive gel,skin allergy,poor flexibility and unstable signal quality of long-term recording for the wet electrode cannot be ignored.Flexible dry electrodes,which replace traditional wet electrodes and have better biocompatibility,have developed rapidly in semiconductor technology.In this paper,based on the current research status of fabrication technology of flexible microneedle array dry electrodes(FMADE),a variety of high density FMADE with 1cm2 area,1-mm-thick polydimethylsiloxane(PDMS)substrate,70～90μm average height of single microneedle and 80～240μm center distance of adjacent microneedles were fabricated by deep reactive-ion etching(DRIE),HNA wet etching and twice PDMS shape-transferring.Aiming at the difficulty of peeling off cured PDMS from wet-etched silicon substrate and the poor adhesion between PDMS and metal layer,a process of depositing 500-nm-thick parylene C film was proposed to solve the above problems.The conformal deposition characteristics of the film can make PDMS more easily and completely separated from wet-etched silicon substrate.Meanwhile,the film can also be used as the adhesion layer between PDMS and metal,which can significantly improve the phenomenon of the metal layer on wrinkles,cracks and drops.In this paper,polymer substrate materials commonly used for flexible dry electrode and the research status of the recent FMADE is firstly introduced,and we propose a PDMS-based FMADE for long-term ECG recording.Then,the constitutive model and simulation parameters of the skin superelastie material are determined by analyzing the structure and mechanical properties of the skin,and the mechanical behavior analysis and finite element simulation of the contact process between a single microneedle and the skin are carried out,and the variation trend of the single microneedle stiffness and penetration force as well as the variation trend of penetration force and penetration displacement are obtained.By the design of structure,process layout and scheme of the FMADE,we develop a set of preparation process flow with simple process,low cost,good material biological compatibility and mass production.Observation of the preparation process by scanning electron microscopy(SEM)indicates that the morphology of the silicon columr arrays and the PDMS microneedle arrays are ideal,but the morphology of the silicon microneedle arrays is controlled by the corrosive liquid ratio.Finally,the key performance comparison tests of the FMADE,wet electrode and flexible planar dry electrode are tested.The comparison results show that the FMADE has some advantages of the smaller and more stable ESCI,the larger and relatively stable signal-to-noise ratio(SNR),and the clearer ECG waveforms,which is suitable for long-term ECG monitoring.